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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 6 |
| 5 | 24 |
| 6 | 120 |
| 7 | 720 |
| 8 | 5040 |
| 9 | 40320 |
| 10 | 362880 |
| 11 | 3628800 |
| 12 | 39916800 |
| 13 | 479001600 |
| 14 | 6227020800 |
| 15 | 87178291200 |
| 16 | 1307674368000 |
| 17 | 20922789888000 |
| 18 | 355687428096000 |
| 19 | 6402373705728000 |
| 20 | 121645100408832000 |
| 21 | 2432902008176640000 |
[0,0,2,6,24,120,720,5040,40320,362880,3628800, 39916800,479001600,6227020800,87178291200, 1307674368000,20922789888000,355687428096000, 6402373705728000,121645100408832000, 2432902008176640000] |